The US-based Centers for Disease Control and Prevention says regular hand washing “is one of the best ways to remove germs, avoid getting sick, and prevent the spread of germs to others”.

According to a scientific study published by the US National Center for Biotechnology Information, one gram (0.03oz) of human faeces – about the weight of a paper clip – can contain one trillion germs.

Bacteria that can be spread by unwashed hands include salmonella and E coli.

US President Donald Trump – who has given more interviews to Fox than any other major network – has admitted on several occasions to being a germophobe.

In his 1997 book, The Art of the Comeback, Mr Trump wrote: “One of the curses of American society is the simple act of shaking hands, and the more successful and famous one becomes the worse this terrible custom seems to get.

“I happen to be a clean hands freak. I feel much better after I thoroughly wash my hands, which I do as much as possible.”